Low frequency tuning system



Sept. 8, 1942. w. R. KocH LOW FREQUENCY TUNING SYSTEM Filed July 31, 1941 Qmkw www@ SSS W IMINIMWVI i..lllllllll Il...

ttorneg A a combined television broadcast or low frequency signal receiving sys- 4broadcast band tuning.

Patented Sept. y8, 1942 UNITED 1 s'ra'rlzs ,PArENr orne A I Low mouai's'mo srsrElvr I wiheid 1r. noch, Haddonneld, N. J., assignor to Radio Corporation of America,v a corporationr of Delaware Appuestioruly 31, 1941, serial No. 404,797

6 Claims. This invention relates to a low frequency or broadcast signal tuning system for adapting a television or other high frequency receiver to be used for broadcast or low frequency reception,

and has for its primary object to provide an imsystemof this character.

proved andsimplied It is also an object of this invention to provide or highfrequency and tem, lwherein the lhigh frequency sound I.F. amplier and audio frequency amplifier portion of the high frequency receiver may be utilized for broadcast reception with minimum apparatus,

anedy detector circuit 28 and a push-pull detector comprisingtwo amplier-tubes 21 and 2l land 34 at. the input and output ends, between v which`are interposed two neutralized piezoelectric crystals 35 and 36 in series together with a resonant circuit 31 connected in shunt across the illter, providing for the transmislson of signals @from the detector 21-28 tothe circuit-20 in Aa and with effective selectivity with a tunable os" cillator circuit alone in The invention will be further understood from the following description when considered in ,con-

nectionwith the accompanying drawing, and its scope is pointed out in the In the drawing: Figure 1 is a schematic appended claims. circuitdiagram of a signal receiving system embodying ,the inven-A tion; and A Figure 2 is a similar schematic circuit diagram the low frequency or' predetermined frequency band such as that indicated, suitable for application to the I.F. am-

l'plifler of the sound channel of the television re- A ceiving system.

Assuming a television I.F. amplifier for sound signals to havea response frequency of the 'order of a portion of the circui/ of Fig. 1 showing a modification thereof.

Referring to Fig. 1, 5 isa'television receiver comprising alfirst detector-'6, an oscillator 1, a picture I.F. amp 1ier and second detector a video amplifier S and/a suitable viewing tube I0, which mcy be of .the. type indicated in the drawing, known'in the commercial market as a Kinescope. The deiiecting and synchronizing circuits may be considered tobe part of the video amplifier indicated in the drawing. The remain# der of the television'receiver includes a sound I.F. amplier and second detector II, an audio frequency amplifier I2 coupled thereto and a suitable loudspeaker device I3.

'I'he first detector is coupled through the input circuit.l4 and a coupling transformer I5 to a diode or other suitable antenna I6, and is pro-` vided with output circuit connections Il-I8 for the picture and sound channels. The sound channel is provided with a'switch I 9 for connecting'the input sideof the sound I.F. amplier to an auxiliary inputcircuit 20 which -forms the output circuit for broadcast or low vfrequency tuning system 2|. Signals are applied to. the

low frequency tuning system, preferably althoughl not necessarily from the same antenna system- I6. In the present example; a tap connection 22 on the dipole circuit connects the dipoles in parallel to the low frequency linput circuit 23-24.

The latter is of the fixed band pass type for liml iting the signal response of the system to a dej sired frequencyrange, such as theA frequency range between 550 and 1600 kc., for example..

The output circuit connection 25 from the band pass lter input circuit is connected to a balcircuit 26 of the detector to cast or low frequency reception in the range of lstraight-line frequency of 8 megacycles,'and passing a band of signals of they order of kc. in width, it has been found that this channelmay not be madevsufllciently sharp, that is .it may knot have sulcient selectivity by utilizing electrical circuits to be used as, the intermediate frequency amplifier of` a broadcast receiver. However, by providing an input system as shown, including the band pass filter 32, sumcient selectivity may be secured for reception of signals in the low frequency or Abroad- With the input system shown and the relatively high frequency I.F. amplifier as here provided, tuning in a low `or broadcast frequency range by means of the oscillator circuit only is made, possible. Thus a simple, inexpensive tuning unit may be provided` including an oscillator circuit tuning inductance 4l and a pacitor 42 in connection therewith.V 'I'he oscillator circuit may be coupled in any suitable manner such as by the inductance 4I, with the input tire unit may be of relatively small size occupying" a minimum of space in the television receiver. Y

Push button control for preselected tuning may likewise be provided in connection with thel oscilmedium of suitable P switching indicated at 44 for placing in circuit lator circuit through the .*push button tuning unit indicated at; 4s comprising. selector switchesy 46 and individually suitable variable tuning zcaprovide for broadthe television or high frecalibration, and the en-.

or variable reactance control tube indicated schematically at 48 in conjunction with the oscillator circuit and controlling the oscillator frequency in the usual manner through an'adjustable bias control'means` I9 for the tube 48, re-

mote tuning control of the oscillator may be effected. While such control of the oscillator in a limited frequency range is common in automatic frequency control systems, the control .heremay provide full tuning of the receiving system for broadcast reception in a wide frequency band.

When reception in the low frequency or broadcast channel is desired, the switch I9 is connected with the circuit and at the same time the picture and video amplifiers may be deenergized by suitable control switches indicated at 50 and 5|. These may be interconnected with the switch I9, as indicated lby the dotted connection 52.

From the foregoing description, it will be seen that only the oscillator of the low frequency or broadcast tuning system requires tuning, and that by utilizing a piezoelectric resonator controlled filter between the broadcast or low` frequency detector and the high frequency I.F., amplifier, sufficient jselectivity may be secured for operation ofthe system with only a band pass filter yinterposed between the signal source and the input side of the detector.

Thus, a simple, inexpensive unit consisting of a band pass lter for the low frequency band, a detector with an adjustable frequency oscillator, and a crystal filter permits low frequency or broadcast/,reception in connection with a relatively wide band and relatively high frequency I.F. amplifier and .the subsequent circuits, including the sound channel of the high frequency receiver.

I claim as my invention:

l. The combination with a signal receiving system having a high frequency broad band signal amplifier, of a balanced detector circuit for signals in a low frequency receiving band, means i including a high frequency .band pass filter providing a balanced output circuit for said detector, said filter comprising piezo-electric reso- 3. In a signal receiving'l system, the combination with a main signal amplifying channel and a high intermediate frequency amplifier connected therewith, of an auxiliary signal input circuit for said amplifier, means for connecting said amplifier with said circuit to the exclusion of the main signal channel of the receiver, a low Y frequency broadcast signal channel connected nator elements, means for connecting the high frequncy amplifier tosaid filter as an alternative signal "source, a low frequency band pass filter connected with the balanced detector circuit,l

and means for applying signals to said circuit through said filter.

2. The combination with -a sound intermediate -frequency amplifier fora high frequency receiver, of means` for applying broadcast low frequency signals'thereto comprising a low frequency signal input circuit including a baiid pass filter, a balanced detector circuit connected with -the output end of said filter, a high frequency oscillator coupled to said detector, said oscillator being tunable in a predetermined high frequency band for producing an intermediate frequency signal within the pass band of said amplifier, a balanced output circuit for said detector,- a high frequency band pass filter including piezo-electric resonator elements connected with said output circuit, and a circuit for connecting the output end of said last named filter to the input end of said high frequency amplifier.

with said circuit, a signal converter in said last named channel including means for tuning said channel within a predetermined low frequency band, a band pass filter preceding said converter in said last named channel, and a high frequency band pass filter including piezo-electric resonator elements interposed between said converter and said auxiliary input circuit.

4. 'I'he combination with a signal receiving system having a high intermediate frequency broadband amplifier, of a tuning system comprising a band pass filter responsive to signals in a relatively low frequency band,` a balanced signal detector connected therewith, a high frequency oscillator coupled to said detector and including variable tuning means eective to cause the frequency of the oscillator to be varied in a predetermined high frequency range to provide an intermediate frequency falling within the pass band of the said intermediate frequency amplifier, and a piezoelectric resonator filter circuit interposed between said detector and said intermediate frequency amplifier for confining the output response of said tuning system within the pass band of said I.-F. amplifier.

-5. The combination with a signal receiving system having a high frequency broad band signal amplifier, a balanced detector circuit forlsignals in a low frequency receiving band, means including a high frequency band pass filter providing a balanced output circuit for said detector, said filter comprising piezo-electric resonator elements, means for connecting the high frequency amplifier to said filter as an alternative signal source, a low frequency band pass filter connected with the balanced detectorcircuit, means. for applying signals to said circuit through said filter, a high frequency oscillator coupled te said balanced detector circuit, and means for tuning said oscillator in a predetermined high frequency band to convert signals in the low frequency signal band into high frequency signals within the pass bandA 6. The combination with a sound intermediate v frequency amplifier for a high frequency receiver, of means for applying broadcast low frequency signals thereto comprising a low frequency signal input circuit including a band pass filter, a balanced detector circuit connected with the out`put end of said filter, a tunable high frequency oscillator coupledto said detector for producing an intermediate frequency signal within the pass band of said amplifier, a balanced output circuit for said detector, a high frequency band pass filter including piezo-electric resonator 'elements connected with said output circuit, a circuit for connecting the output end of saidlast named filter to the input end of said high frequency amplifier, said high frequency band pass filter having a tuned input'circuit, a tuned output circuit, and a pair of series connected piezo-electric 

